1. Field of the Invention
The present invention relates to a plug cutter and, more particularly, to a plug cutter having a dual taper, radial relief to minimize burning of the outer surface of the plug and to avoid premature plug breakaway, and/or a depth stop for plug height repeatability.
2. Description of the Related Art
Conventional plug cutters include a main body portion, a shank extending from one end of the main body portion, and a plurality of cutting tines, or blades, extending axially from an opposite end of the main body. The plurality of cutting blades define a bore that is circular in cross section. The configuration of the bore corresponds to the configuration of the plug produced with the plug cutter.
Typically, a plug cutter is produced by first, drilling a bore axially into a cylindrical piece of steel and, second, milling the cutting blades out of the resulting annular wall surrounding the bore. Each blade has an inner surface that faces radially inwardly toward the center of the bore.
Contact by the entire inner surface of the blades on the outer surface of the plug while the plug cutter is rotating can cause burning on the outer surface of the plug due to the heat generated by the high speed frictional contact of the inner surface of the blades with the outer surface of the plug. In addition, friction between the outer surface of the plug and the inner surfaces of the blades can cause a torque to be applied from the plug cutter to the plug, causing the plug to prematurely break away from the stock and become lodged in the bore of the plug cutter. In this case, the plug can only be removed from the plug cutter by destroying the plug. Finally, if the entire inner surface of the blades contact the outer surface of the plug, the outer surface is formed by shearing, rather than cutting, resulting in a plug having a rough outer surface.
The present invention avoids the above-described disadvantages encountered with conventional plug cutters by providing a measure of radial relief between the inner surface of the blades and the circular bore defined by the leading, cutting edges of the blades. The present invention further advantageously defines a dual taper to provide an increased taper at the top periphery of the plug to ensure snug engagement of the formed plug with the bore in which it is inserted. Furthermore, the preferred embodiment of the present invention further provides the unique advantage of an integrated depth stop in the plug cutter bore for providing the plug height repeatability and quick set-up that is highly desirable for woodworking tasks.
Therefore, according to the present invention, a plug cutter is provided that is rotatable about an axis of rotation. The plug cutter comprises a main body having a longitudinal axis coinciding with the axis of rotation, a shank coaxial with the axis of rotation extending from one end of the main body and a plurality of cutting tines or blades extending axially from the opposite end of the main body. The plurality blades are adapted to cut a plug in a piece of stock material as the plug cutter is rotated at high speed about the axis of rotation and advanced axially into the piece of stock material. In one exemplary embodiment, each blade is formed so that an inner surface thereof defines a dual taper portion adjacent and along a leading edge of the blade, with respect to the direction of rotation, and a radial relief portion downstream of the dual taper portion. The radial relief portion comprises a portion wherein the radial distance from the axis of rotation to the inner surface of the blade is greater than a radial distance to said dual tapered surfaces or to said cutting edge so that as the plug cutter is cutting a plug, substantially only the cutting edge and the dual tapered portions of each blade make contact with the outer surface of the plug. According to a further feature of an exemplary embodiment of the invention, a depth stop is defined within the bore of the plug cutter to limit the height of the plug produced, for plug reproducibility and to avoid plug jamming within the plug cutter.